The invention relates to asphalt compositions. More specifically, the invention relates to asphalt compositions containing catalysts for the air-blowing of asphalt.
The asphalts in unprocessed form, i.e. naturally occurring or from petroleum refining, may be unsuitable for a given application because of excessive brittleness, insufficient penetration at a given softening point, and the like. A technique known as "air-blowing" was developed to modify the properties of the asphalts so that a desired penetration at a desired softening point can be achieved. Air-blowing raises the penetration of the asphalt at a given softening point.
Air-blowing is a process in which the asphalt is subjected to heat and mixing in the presence of a gas, such as air, oxygen or oxygen and an inert gas, and optionally a catalyst. The process raises the softening point and lowers the penetration of the asphalt.
Phosphorous sesquisulfide (P.sub.4 S.sub.3), phosphorous pentasulfide (P.sub.2 S.sub.5), H.sub.3 PO.sub.4, P.sub.2 O.sub.5 and ferric chloride (FeCl.sub.3) are known asphalt air-blowing catalysts. Since the process of air-blowing is energy intensive and the catalysts can be expensive, it would be highly desirable to have an air-blowing catalyst which can be used in lower concentration than, for example, ferric chloride and/or exhibit an increased penetration point for a given softening point. It would also be desirable to have a catalyst with a lower chlorine content than FeCl.sub.3, as the HCl which is given off as a byproduct can cause corrosion of metal vessels and contribute to air pollution. Increasing the penetration point at a given softening point gives a product which is flexible at low temperatures but does not flow at ambient temperatures.